TMF Design Optimisation for Automotive Turbochargers Turbine Housings

Turbine housings for automotive turbochargers are complex castings that are subjected to transient thermal stress from exhaust gas temperature and flow variation under complex duty cycles. A fatigue model based on a cumulative damage approach (Chaboche model [1]) is used to predict crack initiation. As the stress varies with temperature, a modified Chaboche model based on a normalized stress is proposed. To determine the transient stress and temperature distributions due to the high rates of convection from the gas, and the complexity of the design, conjugate heat transfer CFD simulation is performed. The tongue of the turbine housing is a critical region in which cracks initiate within a short time. Heat transfer coefficients ( HTC ) and bulk temperature predictions from CFD, in general, can be validated by thermal measurement. But because of the geometry and the location of the tongue, it is impossible to measure the metal temperature. For this work 2 methods were presented: HTC calibrated by thermal measurement and HTC from CFD heat transfer Conjugate method, steady state analysis. Heat transfer Coefficients and bulk temperatures obtained with those 2 methods are different. The heat transfer from CFD analysis with 15 layers has an important HTC which is 3000 W/ m² °C, it is equal to 1200 W/m² °C for the calibrated method, but the bulk temperatures are not the same. A sensitivity study on predicted life shows that this difference results in no more than a 2 hr change for a total predicted life of 50 hrs. In the industrial approach this difference is quite acceptable. The design of a turbine housing is optimized based on this TMF methodology and shows very good results in testing, as presented here.